RE: sizeof problem in kernel modules

[Anil Kumar]

struct { short x; long y; short z; }bad_struct;
struct { long y; short x; short z; }good_struct;

I would expect both structs to be 8byte in size , or atleast the same size !
but good_struct turns out to be 8bytes and bad_struct 12 .

what am I doing wrong here ?

thx !
hofrat
///////////////////////////////////////
It's general padding performed everywhere for a 32-bit m/c. Since the short
number is considered to be of 2 bytes whereas new data should start at the
next 32 bit alignment( if the data length exceeds the padding required )
hence next 2 bytes are left as padding, so the actual struct. of your
defined structutres are as follows,

struct{
 short x; /* 2- bytes */
 /* again 2- bytes padding */
 long y;  /* 4 - bytes */
 short z; /* 2 - bytes */
 /* again 2 - bytes padding
}bad_struct;

struct{
 long y;  /* 4 - bytes */
 short x; /* 2 - bytes */
 short z; /* 2 - bytes */
}good_struct;

anil